1. Field of the Invention
The present invention relates to a taking lens apparatus. More specifically, the present invention relates to a taking lens apparatus (a main component of a digital camera, video camera, or camera incorporated in or externally fitted to a personal computer, mobile computer, cellular phone, personal digital assistant (PDA), or the like) that optically takes in an image of a subject through a taking lens system and that then outputs it in the form of an electrical signal by means of an image sensor, and in particular to a taking lens apparatus incorporating a compact zoom lens system as its taking lens system.
2. Description of the Prior Art
In recent years, digital cameras, which use an image sensor such as a CCD (charge-coupled device) instead of silver halide film, have been rapidly becoming increasingly popular. On the other hand, as the image processing power of semiconductor devices and the like increases, cameras using an image sensor have come to be increasingly incorporated in cellular phones, PDAs, and the like. Under these circumstances, further compactness is sought in taking lens apparatuses used to take an image of a subject and outputs it in the form of an electrical signal by means of an image sensor. In addition, sought nowadays are not simple taking lens apparatuses like those conventionally common, but taking lens apparatuses that offer high resolution combined with correspondingly high optical performance and optical zooming with minimum image degradation in order to achieve photographing with high image quality. However, attempting to make a taking lens apparatus compact by reducing the weight and size of a taking lens system makes it difficult to maintain satisfactory optical performance. To overcome this inconvenience and meet the above requirements, various types of zoom lens system have conventionally been proposed. For example, the following patent publications propose zoom lens systems in which, with a view to realizing a compact taking lens apparatus, the optical path is bent with a prism inserted between lens elements.                A. Japanese Patent Application Laid-Open No. H8-248318        B. U.S. Pat. No. 6,104,432        
However, with the zoom lens systems proposed in these publications, it is difficult to meet all the requirements mentioned above simultaneously. For example, the zoom lens system proposed in Publication A has a four-unit zoom construction of a, from the object side thereof, positive-negative-positive-positive type, and includes a large number of lens elements, making it impossible to achieve satisfactory compactness along the optical axis. The same is true with the zoom lens systems proposed in Publication B, which also include a rather large number of lens elements including a prism, making it impossible to achieve satisfactory compactness.